What it will probably boil down to is just making whatever you pick work for you. Everything you've mentioned will fly the plane very well. You may be thinking about a first 4-stroke but it won't likely be the last. You can always try somethign else down the road.

As for the OS 4-strokes, several people have commented that my .91 is not enough for my TF Mustang how the Saitos are supposedly much better, etc. It has a good prop and is tuned right however and most change their opinion after seeing it in the air. It hauls the plane around very nicely.

Saito, OS, Thunder tiger, it'll all work well.